ChemInform Abstract: Electroluminescence at n‐SiC/Electrolyte Interface Under Cathodic Polarization. Observation of EL Transients in a Short Time Scale and Further Evidence for a Donor‐Acceptor Transition

Abstract

Electroluminescence (EL) at electrolyte junction was studied under cathodic polarization. Various redox electrolytes including current doubling reagents like persulfate were employed to understand the nature of EL. When the cathodic bias is higher than the flatband potential of electrode, species like persulfate are reduced by the conduction band electrons to form highly oxidizing intermediates which inject holes into the valence band to produce light . In the case of redox electrolytes like , , etc., the EL emission is weak and occurs at a higher cathodic bias, i.e., when the cathodic bias exceeds the bandgap energy of . Here, an electron transfer occurs from the valence band to the redox electrolyte. This indicates that the minority carrier injection (hole) is an important process in obtaining high EL intensities. The emission appears greenish‐yellow and the peak energy of the spectrum is smaller by 1.1 eV than the bandgap of (3.2 eV, calculated from photoresponse measurements), suggesting that the radiative recombination occurs through the impurity luminescent centers. Even under continuous polarization the EL intensity is steady for longer time duration and the electrodes are highly stable. The spectral distribution and increase in the EL intensity with different cathodic pulsed bias potentials were observed and explained by a donor‐acceptor (D‐A) mechanism. The charge transfer at the interface and the radiative recombination of electrons and holes inside the semiconductor are explained from the characteristics of EL and current intensities vs. time obtained under various pulsed polarized conditions. Moreover, the electrodes are highly stable under cathodic steady‐state polarization for several hours. Time resolved measurements (using our present system) seem to indicate the EL transients are limited by the current flow.